Discussion On "Strong Column Weak Beam" Of RC Frame Structure

The design target of “strong column weak beam” stipulated in the current seismic code of our country is difficult to achieve in the seismic design of public buildings(such as schools and office buildings).The main reason is the installation of half-height continuous infill walls make the actual stiffness of beams increased greatly and the short column is formed,which causes the structure to be destroyed by “strong beam weak column” in actual earthquake.In this paper,the shaking table test is performed according to the actual earthquake damages,and the method of combining theoretical analysis and experimental research is used to study the damage and collapse mechanism of RC frame structure with half-height infill wall.The results are of great value in guiding the seismic design of the related the related structures.Based on the overall collapsed Xuankou middle school teaching building in the Wenchuan earthquake,two structural models with a scale ratio of 1/4were established.Shaking table test was used to study the main reasons for the failure of the “strong beam weak column” of the half-height infill wall frame and the method of collapse reinforcement of this kind of building structure.The main results are as follows:(1)This paper summarizes seismic damage characteristics and the current research situation of RC frame structure with half-height infill wall.The concept and the development history of the “strong column and weak beam”design theory is summarized.(2)The seismic damage of RC frame structure based on the theory of "strong column weak beam" is analyzed.The collapse force mechanism and resistance distribution law of a typical RC frame structure designed according to China's regulations are studied,which provides a basis for further research on the design method of anti-collapse.(3)Taking the Xuankou Middle School Teaching Building as a prototype,a RC frame model with a scale ratio of 1/4 is established.Before the infill wall is set up,the RC frame model is subjected to modal testing,percussion testing and excitation testing.Under the condition of no infill wall,the shear force of the bottom column is evenly distributed,and the bending moment at the end of the column is much larger than the moment at the beam end.The modal test and seismic simulation test are carried out after the infill wall is set up.The strain curve of the half-height infill wall is in good agreement with the strain curve of the column end.It shows that the half height-infill wall works together with the frame beam and column,forms the wall beam,increases the bending stiffness of the beam end,and leads to the appearance of the failure mode of "strong beam and weak column".(4)A reinforcement method of adding wing walls on both sides of the frame structure column is proposed,and a shaking table test is performed by using the Xuankou middle school teaching building as a prototype to establish a model structure with scale of 1/4.The experimental results show that the addition of wing walls can effectively distribute the stiffness of the longitudinal axes of the structure,and the seismic forces are evenly distributed.The structural damage plastic hinge appears at the beam ends,and the “strong column weak beam” failure mode appears.Based on the above experimental phenomena and the analysis of failure modes,some suggestions are put forward for the design and reinforcement of RC frame structures with infill walls under earthquake.